Field of the Invention
The invention relates to a method of Doppler ultrasound images clustering, noise reduction and visualization. In particular, a method implemented in an image processing system for Doppler ultrasound images.
Descriptions of the Related Art
Receiving of ultrasound images may be distinguished as power Doppler ultrasound image and color Doppler ultrasound image. Power Doppler ultrasound image shows complete artery and vein image, but it does not have direction information on blood flow. Nevertheless color Doppler ultrasound image only shows indirect direction information on blood flow. Otherwise, noise in the Doppler ultrasound images caused by the motion artifacts is also a critical problem for explaining the blood flow information. Thus, some patients should keep stationary during the Doppler examination because breathing may produce motion artifacts. Additionally, there are probe motion artifacts which may be arisen by using a hand-held probe (called a transducer) which is placed directly on and moved over the patient. Therefore, it is necessary to provide a suitable noise-reduced Doppler ultrasound image for evaluating the completely pulsatile information on blood flow.
In the prior art, Taiwan Patent No. 1275,383 in and U.S. Pat. No. 8,047,993 B2 disclose a non-invasive measurement method of tumor hemodynamic parameters to detect the degree of malignancy in tumors. The method comprises the steps of: using a power Doppler ultrasound unit to scan a tumor and capture sequential color images in a heartbeat cycle, and choosing an area of interest (AREA_ROI) from the images, labeling pixels reflecting signals of blood flow in the images during one heartbeat cycle to contour an area of tumor blood vessels (AREA_vessel); calculating a difference of PDVI between maximal systolic pressure and diastolic pressure during the heartbeat cycle to obtain tumor differential vascularity index (TDVI), in which PDVI is the ratio obtained by dividing pixels of AREA_vessel by total area in the section of AREA_ROI to determine the degree of malignancy by the TDVI. It can be applied to clinical diagnostic.
Furthermore, U.S. Pat. No. 8,047,993 B2 discloses a method for evaluation of renal perfusion with power Doppler ultrasonography. Serial renal vascular images at different vascular areas including the whole vascular tree, interlobar, arcuate, and interlobular vessels were captured. Imaging processing software was designed to analyze the changes of power Doppler intensity of colored pixels within regions of interest (ROI). Power Doppler Vascularity index (PDVI) has been defined as the percentage of vascular perfusion within a region of interest (ROI). The renal vascular perfusion index (RVPI) was defined as the maximal power Doppler vascular index which divided by minimal power Doppler vascular index (PDVI max/PDVI min) among the serial images. The mean of weighted power Doppler vascular index (WPDVI mean) was defined as the average of the intensity of colored pixels among the ROI within the serial images. By using the RVPI and WPDVI mean, a more dynamic sense of vascular perfusion and a novel approach for the evaluation of renal vascular function in clinical practice can be provided.
However, TW 1275383, U.S. Pat. Nos. 8,047,993 B2 and 8,777,860 B2 do not disclose clustering methods for evaluation of pulsatile information from blood flow in a sequence of power Doppler ultrasound images and the color Doppler ultrasound images. In particular, the present invention provides a method and system to quantify and classify the color pixels in the Doppler ultrasound images into three groups, namely the primary pulsatile signal, the secondary pulsatile signal, and noise signal based on the intensity changes of each color pixel over the sequence of Doppler ultrasound images. The classified signals will be visualized with different color values. Therefore, methods and systems in this invention provide the noise-reduced pulsatile signal images for reflecting pulsatile information form blood flow in the images, which is intended for vascular pulsatility analysis.